BANGKOK — Thailand seized 4 tons of ivory hidden in bean sacks tracked from Congo in what authorities said was the biggest bust in the country’s history, customs officials said Monday.

The 739 elephant tusks, bound for Laos, were seized upon arrival at a port in Bangkok on Saturday after the authorities received a tip and had tracked the containers from Congo, Customs Department director-general Somchai Sujjapongse told reporters.

He said that the shipment, labeled as beans, was shipped out of Congo in February and went through Malaysia before reaching the Bangkok port.

“We have been following the [shipment] for two months. Intelligence reports said ivory from Africa might be smuggled with other products to go through the Laotian border,” Somchai said.

Thailand is one of the top destinations for African ivory smuggling in Asia and could face international sanctions soon if it doesn’t show progress in combating the problem.

Somchai said authorities believe that if the $6 million worth of ivory had reached Laos, it would then have been distributed to buyers in China, Vietnam and Thailand.

Poachers have killed tens of thousands of African elephants for their tusks in recent years to meet demand for ivory in Asia. China has imposed a one-year ban on ivory imports amid criticism that its citizens’ huge appetite for ivory threatens the existence of Africa’s elephants.